1. Field of the Invention
The invention is directed to a method for setting a plurality of controllers for controlling a process controlled system composed of coupled control systems.
2. Description of the Related Art
In commonly used control systems without decoupling filters, as can often be encountered in practice, independent control systems are assumed for simplification for using manual initialization. Existing couplings between control systems can usually not be clearly recognized and are therefore frequently ignored. When, however, such couplings between control systems exist in application, then the initialization or readjustment of a control system affects other control systems in the overall control system.
In this situation the manual setting is accomplished in a plurality of steps, in which parameters of a controller are modified in order, to quickly compensate a rated value different when setting a new rated value, among other things moreover when, an overshooting can occurs in the control circuits, the controller parameters must be readjusted in the coupled control systems, so that the control circuits work satisfactorily. Each-therefor adjustment of the controller parameters in a control system clearly effects a modification of the control circuits in the control systems that have a coupling (of different extents) to the adjusted control system. When a process controlled system contains a plurality of control systems, the initialization is a lengthy and tiresome one must wait for the stationary condition of the overall process control system before every modification and control circuits that are already set are readjusted with progressive initialization due to the modifications of other controllers.
In a processed controlled system composed of a plurality of control systems, the object of the invention is to undertake a setting of the in which therefore, only measured values for the transient response of the systems are employed in order to be able to set the parameters of the controllers all at once.
This object is achieved a method for setting a plurality of controllers for controlling a process controlled system having coupled control systems, comprising the steps of determining a transfer function from a type of a respective controller, implementing, for each control circuit, measurements of setting signals and output signals of the process controlled system, determining, from these measurements, transfer functions for the coupled control systems contained in the process controlled system and their couplings, calculating, for each controller, an equivalent path that utilizes the couplings with other control systems in the process controlled system, and iteratively determining, for each respective coupled control system, controller parameters utilizing couplings with the other control systems for each respective controller until a predetermined quality has been reached.
With the inventive method, the respective controller parameters are calculated for each controller in a process controlled system composed of a plurality of control systems, in which the measured values for the transient response of the process controlled system are necessary in order to automatically determine all of the control parameters. The initialization of, for example, a furnace that is composed of a plurality of heating zones is thus accomplished in one step, since the manual iteration is eliminated because this initialization is automatically implemented on a computer. This implementation is possible because the couplings are also taken into consideration in the inventive method and, in contrast to the manual setting method, the controller parameters are modified based on the behavior of multiple control system. A considerable time saving is achieved because the required iterations for optimizing the controllers are implemented in a computer. Transient response events of temperature control systems can be simulated significantly faster on computer.
A further advantage of the invention is that controller settings can be reproduced and are thus less dependent on the experience level of the person undertaking the setting.
In general, automatic optimization is more economical than the described, manual iteration method, since resources are not wasted.
The automatically determined controller settings lie in the immediate proximity of a possible optimum setting, which enables an economical operation of the system.
Further, the automatic design method supplies a xe2x80x9creferencexe2x80x9d that can be employed for judging an optimization potential of a complex system.
It is an additional advantage of the invention that the noise behavior is also taken into consideration in the automatic controller setting. This contrast with the manual controller settings which are frequently only undertaken for the management behavior.
Further, it is also possible to reduce the plurality of required iterations on the computer by utilizing modern numerical methods.
A transfer function is determined for each controller A PID controller has the typical controller parameters xe2x80x9cproportional part Pxe2x80x9d, xe2x80x9cintegrating part Ixe2x80x9d and xe2x80x9cdifferentiating part Dxe2x80x9d available to it. In control technology, the corresponding transfer function for different types of controllers are adequately known to a person skilled in the art, usually in frequency-dependent presentation with Laplace operators s=jxcfx89.
As mentioned, measurements are implemented at the process controlled system, in which a transient behavior is registered for each control system to be taken into consideration. The transient behavior of each control system in the process controlled system is thus available and one knows the type of controller. An equivalent system is now calculated that takes couplings of the respective control system with other control systems into consideration. By knowing of this control system, it is possible to calculate the controller parameters for each controller of a control circuit in iterative steps, in which a separate presentation of the controller parameters dependent on other controller parameters exists for each control system and, as a result of the computer, the proper controller parameters for each control circuit are respectively identified with the controller parameters of the coupled control systems that have already been calculated. These parameters enter into the other equations that comprise a coupling to the control system. In a next step, the controller parameters of the next controller are optimized, etc.
One development of the invention is comprised in calculating the controller parameters for the respective controller of a control system in that a zero point search of a presentation present in implicit form that contains the transfer functions of all controllers, systems and couplings is implemented, whereby an iterative Newton method can also be applied.
Another development of the invention is comprised in implementing the setting of the plurality of controllers of the process controlled system with non-linear controller parameterization methods, preferably with a neural network (neural controller parameterization method).
One application of the inventive method is in an initialization of a furnace composed of a plurality of heating zones, e.g., for burning bricks, in which fixed demands are made of the temperature curve within the furnace.
Other applications of the invention are for combined pressure/flow controls in supply lines or temperature/humidity controls in air conditioning systems.
One development of the invention is comprised in the use of a processed control system that is composed of at least two control systems and is controlled with at least two controllers.
Developments of the invention are discussed below.